Spectrums are a foundation of wireless communication. According to the latest International Spectrum White Paper issued by FCC (Federal Communications Commission), unlicensed frequency band (also referred to as unlicensed spectrum) resources are more than licensed frequency band (licensed spectrum) resources. Therefore, LTE (long term evolution,) user equipment is applied to an unlicensed frequency band. For example, a licensed-assisted access using Long Term Evolution (LAA-LTE) system can not only efficiently utilize the unlicensed frequency band but also provide more efficient wireless access to meet an increasing requirement for mobile broadband services.
To ensure friendly coexistence of systems and devices that perform communication on the unlicensed frequency band, a listen before talk (LBT) channel access mechanism is introduced in some countries and regions, such as Europe and Japan. A basic idea of LBT is as follows: Before sending a signal on a channel, each communications device needs to detect whether the current channel is idle, that is, whether a neighboring node is occupying the channel to send a signal. This detection process is referred to as clear channel assessment (CCA). If it is detected that the channel is idle in a period of time, the communications device can send the signal. If it is detected that the channel is occupied, the communications device currently cannot send the signal.
One unlicensed frequency band generally includes a plurality of carriers. Therefore, an LTE device (such as an LTE eNodeB) may send data simultaneously on a plurality of carriers according to a carrier aggregation capability of the LTE device, that is, may contend, on the plurality of carriers by means of LBT, for an opportunity to use an unlicensed frequency band corresponding to the plurality of carriers. Carriers other than the plurality of carriers on the unlicensed frequency band go beyond the carrier aggregation capability of the LTE eNodeB. Therefore, the LTE eNodeB does not send data on these carriers, that is, may not use these carriers as operating carriers in a period of time. In addition, for user equipment served by the LTE eNodeB, a carrier aggregation capability of the user equipment is usually smaller than the carrier aggregation capability of the LTE eNodeB. Therefore, the user equipment can perform data transmission with the LTE eNodeB only on some carriers in the plurality of carriers. The present disclosure is to resolve a problem about how to design an appropriate measurement mechanism so that the LTE user equipment can accurately distinguish between wireless conditions corresponding to different carriers.
In the prior art, the user equipment separately measures interference energy in an active period and an inactive period of a serving cell. The active period of the serving cell is corresponding to a time period (also referred to as a time resource) in which the serving cell preempts an unlicensed frequency band, and the inactive period of the serving cell is corresponding to a time period in which the serving cell does not preempt an unlicensed frequency band. That is, according to this method, the user equipment can measure interference energy only of the serving cell in different time periods, but cannot learn an active period and an inactive period of another cell (for example, a neighboring cell). Therefore, the user equipment cannot measure interference energy of the another cell in different time periods. This affects obtaining of a comprehensive interference energy measurement result and further affects mobility performance of the user equipment. The mobility performance includes serving cell selection.